Stunfisk is capable of checking Tornadus-Therian, Zeraora, Tapu Koko, and maybe even Heatran once over. With SR and dual STAB, it is still on the passive side, but with Wish support and something to check the other things Landorus-T or Garchomp otherwise would, it would not be the worst thing to use on a balance.
Stunfisk-Galar is perhaps a bit tougher, but you still check Tapu Koko and you can throw in Snap Trap + Yawn shenanigans. It would not be advisable, but again it is not the absolute worst Pokemon.
With this said, both would be strictly defensive and on the passive end, so proceed with caution.